Code suggested that PLL with MSI is used resulting in 80MHz clock.
When in fact PLL was not configured and system clock was left at MSI 48MHz.
This happens because PLL configuration requires that SysTick interrupt
has interrupt priority level configured correctly.
As it seems ST code intentionally setups variable uwTickPrio to invalid
value and later when it is not setup by user code configuration
of oscillator will fail before PLL is configured.
This simple changes systick priority to some valid value that
allows clock to use PLL.
Field PLLState was not initialized in RCC_OscInitStruct.PLL in
function SystemClock_Config().
Value is used in HAL_RCC_OscConfig() regardless of oscillator.
In lucky case value would be 0 RCC_PLL_NONE and nothing would
happen.
If value was incorrect following line would end up in assert:
assert_param(IS_RCC_PLL(RCC_OscInitStruct->PLL.PLLState));
If value was valid but no RCC_PLL_NONE pll could be configured
with some other random values.
Setting PLLState to RCC_PLL_NONE eliminates potential problem.
